MOEPHOLOGT OF THE OWLS. 9 



the aperture in question lies considerably behind this process. From the aperture there 

 runs, backwards and downwards, a vestigial temporal fossa, also corresponding to that of 

 the left side. 



The tympanic cavity of JPhotodiltcs and the Strigidse is of the same type as that found 

 in Asio. Indeed this cavity in the latter appears to be a further modification of tliat 

 seen in the two subfamilies above mentioned. 



That of Strix is the least specialized of all ; that portion of the cavity which lies above 

 the head of the quadrate, and between the squamosal wing and postorbital process, is of 

 comparatively slight extent, consisting merely of a small depression. In Asio, it will be 

 remembered, it forms a large, oblong, and concave fossa. PhotodUns is intermediate in 

 some respects between the two. In the skull of this form the fossa is nearly as long as 

 in Asio, but very narrow from side to side. In the great size of the postorbital process 

 Photodihis differs both from Asio and Strix. In the development of the squamosal 

 wing it is also peculiar. This is larger than in Strix, smaller than in Asio. Asio, Strix, 

 and Photodilus all agree in the absence of the horizontal temporal fossa so conspicuous, 

 for example, in Puho. 



The orbits in the Asionidfe are large, and their capacity is still further increased 

 by the lateral expansion of the postorbital processes. They are overarched by the 

 frontals, and bounded in front by the lachrymals, whilst the antorbital processes 

 (prefrontals) and the orbital process of the quadrates form an imperfect floor. Feeble 

 supra-orbital processes are commonly, but not invariably, present. These, it is to be 

 noted, are furnished by the frontals themselves, and not, as in the Falconiformes, by the 

 lachrymals. The intei'orbital septum forming the partition wall between the two orbits 

 is imperforate, save in Surnia, Speotyto, and some species of Scops. The orbito- 

 spheuoid is completely ossified. 



The cptic foramina are widely separated one from the other, and lie on a level with a 

 line drawn forward from the bottom of the rim of the recessns tympaniciis superior. 



The trigeminal foramina open above the roof of the recessns ti/nqmnicus anterior on 

 a level with a line drawn downwards and forwards from the anterior zygomatic process 

 to the basiptery golds. 



Immediately external and posterior to the optic foramen lie the foramina of the 

 third, fourth, and sixth nerves. 



The orbit in the Strigidre differs conspicuously from that of the Asionidte and Photo- 

 dilidae in that it is extremely small. Its horizontal axis scarcely, or not at all, exceeds 

 that of the horizontal axis of the lachrymal, though it must be remarked this last-named 

 bone is relatively very much larger than that of the two suborders with which it is 

 contrasted. Even, however, where the lachrymal of the two suborders is relatively as Large 

 as that of the Strigidie, the greater size of the orbit with regard to the lachrymal would 

 still remain the same. 



The Strigidse are furthermore peculiar in having the interorbital septum, which is very 

 short antero-posteriorly, enormously inflated by the development of spongy tissue. 



The Ethmoidal Megion. — The mesethmoid, which by its posterior extension forms the 

 interorbital septum, agrees more nearly with the mesethmoid of the Caprimulgi than 



SECOND SERIES. — ZOOLOGY, VOL. IX. 2 



